We go to WDW every Easter. Crowd levels depend on when Easter falls. This year, 2014, Easter was in later April so crowds were VERY manageable. Not even worthy of saying it was crowded, to be honest, as we went on more rides than we ever have due to lower crowds.
However, when Easter falls in late March/very early April, it's a whole different story. I believe Easter was in this time frame in 2013 and we definitely noticed MK to be crowded. I believe in 2015, Easter is early again, so I'd guess crowds to be heavy especially at MK. But the FP+ system helps with this because you can just pre-book your must-do rides ahead of time.
You are used to crowds at Cmas, Tgiving, and early June, so you should be just fine with Easter week. Especially by utilizing the FP+ system.